An audio signal transmission between an audio interface (e.g., a headphone jack) of a conventional audio signal sending apparatus (e.g., a mobile terminal) and an audio interface of a conventional audio signal receiving apparatus (e.g., a headphone) is generally performed as a single channel transmission or a multichannel transmission, in which a third pin is used as a single-channel audio output pin, or the third pin and a fourth pin are used as multichannel audio output pins, i.e. a left channel pin and a right channel pin. However, the first pin and the second pin of different audio interfaces perform different functions, i.e. there are two types of audio interfaces: one type of audio interface having a first pin as a microphone pin (MIC pin) and a second pin as a ground pin (GND pin), and the other type of audio interface having a first pin as a ground pin (GND pin) and a second pin as a microphone pin (MIC pin).
Due to different types of audio interfaces, when an audio interface of an audio signal sending apparatus (e.g., a mobile terminal) is not matched with an audio interface of an audio signal receiving apparatus (e.g., a headphone, a headset, or an electronic signature token), it is impossible to perform the communication between the audio signal sending apparatus and the audio signal receiving apparatus via microphone pins of the audio interfaces, or to perform the audio signal transmission between the audio signal sending apparatus and the audio signal receiving apparatus via audio output pins (i.e. left channel pins and right channel pins) of the audio interfaces normally.
With the continuous advance of mobile internet technology, the capability of the mobile terminal becomes more and more powerful, and therefore the demand for mobile payment becomes more and more urgent. However, due to the small volume of the mobile terminal, the number of external interfaces is very small, so how to connect the electronic signature token and the mobile terminal has become a serious problem. Especially since there are different types of audio interfaces of the mobile terminal, the successful connection between the mobile terminal and the electronic signature token is hindered. In particular, since the types of audio interfaces of the mobile terminal are various, after inserted into the audio interfaces of the mobile terminal, the electronic signature token may not be identified, so that it is impossible to establish the communication between the electronic signature token and the audio interfaces of the mobile terminal.